The invention relates to a method for operating a volume-controlled internal-combustion engine having an intake tract and an exhaust system, wherein an expansion machine is arranged in the intake tract in a flow direction of combustion air in front of an inlet valve of the internal-combustion engine, as well as to an associated internal-combustion engine.
From German published patent application DE 101 16 264 A1, a method is known for the operation of an internal-combustion engine with mechanical supercharging and variable compression. In the case of the method for the operation of the internal-combustion engine having a mechanical compressor arranged in the intake tract, which mechanical compressor can be driven by way of a coupling device by the crankshaft, combustion air is supplied into an engine intake. Furthermore, a device for the variable adjustment of the compression ratio in the combustion chamber is provided, by way of which a higher compression ratio can be adjusted in the partial-load range of the internal-combustion engine, and a lower compression ratio can be adjusted in the full-load range. The air mass flow to be delivered by the compressor can be adjusted in a variable manner, in which case, in the partial-load range below a reference load value, the compressor is operated in a throttle or expander operation for adjusting a vacuum in the air intake.
Furthermore, the above-mentioned throttle method for internal-combustion engines is known from the book “Turbo- und Kompressormotoren”, Entwicklung und Technik (“Turbo and Compressor Engines”, Development and Technology), Publishers Motorbuchverlag, Hack/Landkabel, 2nd Edition 2001, ISBN No. 3-613-01950-7. This known throttle method is explained in detail in this book, Chapter “Ladertypen im Detail” (“Details about Types of Superchargers”), Page 72, Subchapter “Regelung” (“Control”).
The above-mentioned method has the disadvantage of a not yet sufficient efficiency increase of the volume-controlled internal-combustion engine, which is still clearly below that of a quality-controlled internal-combustion engine, in which the load control takes place, for example, by means of a lean-burning method (λ>1).
It is an object of the present invention to provide a method of operating a volume-controlled internal-combustion engine whereby the efficiency is significantly improved.
With respect to the method, this and other objects are achieved by operating a volume-controlled internal-combustion engine, having an intake tract and an exhaust system, wherein an expansion machine is arranged in the intake tract in a flow direction of combustion air in front of an inlet valve of the internal-combustion engine. An output shaft of the expansion machine is able to be coupled with an output shaft of the internal-combustion engine or with a drive shaft of an electric machine. A heat exchanger that can be arranged in the exhaust system is provided. Before combustion air flows through the expansion machine, it is heated in the heat exchanger by an exhaust gas of the internal-combustion engine. This object is further achieved by a corresponding internal-combustion engine.
It will be demonstrated in the following that, by utilizing the expansion process in the intake tract, not only the charge cycle losses are avoided but, in connection with the exhaust gas heat exchanger according to the invention, clear efficiency advantages and thus significant consumption advantages are achieved. Furthermore, this technology can particularly easily be combined with exhaust gas turbo-charging. In the following, an efficient load control (ELS) of a volume-controlled internal-combustion engine will also be mentioned with respect to the invention.
Similar to the increase of internal-combustion engine power that can be achieved by a (mechanically or electrically driven) compressor in the intake tract by compressing the combustion air, by means of an expansion machine instead of the throttle valve, the combustion air can be “diluted”, i.e. can be adjusted to a lower density and thereby the power of the internal-combustion engine can be reduced. As a result, the throttle losses of a throttle valve are practically entirely avoided. The efficiency advantage is comparable to a variable valve timing, as used, for example, by BMW in mass production under the “Valvetronic” trademark. In that case, the work carried out in the expansion machine can be fed by way of a mechanical coupling (for example, a belt drive) to the internal-combustion engine. So far, this corresponds to the known state of the art.
A further clear rise of efficiency in the partial load of the internal-combustion engine can be achieved in that, according to the invention, thermal energy is transferred to the combustion air by way of a heat exchanger at the exhaust gas system. The volume flow of the combustion air is thereby increased and, proportionally thereto, also the work that is carried out in the expansion machine in the intake tract. On the output side of the expansion machine, the combustion air is cooled again to the normal combustion air temperature by a cooler, such as a charge air cooler, before it is fed to the internal-combustion engine. Efficiencies can thereby be achieved in the partial-load range of a volume-controlled internal-combustion engine, which are clearly above that of a variable inlet valve drive.
Furthermore, the method can be combined excellently with exhaust gas turbocharging (in this case, a charge air cooler is advantageously already present). A portion of the thermal energy in the exhaust gas can be supplied in the form of a pressure increase to the combustion air of the expansion machine while simultaneously reducing the temperature in the heat exchanger. This advantageously results in a lower temperature load on the components in the intake tract. The efficiency-improving operation of the expansion machine can thereby be expanded by a higher pressure difference by way of the expansion machine into higher load ranges of the internal-combustion engine. The theoretical efficiency that can be achieved in a comparison process corresponds to that of a process implementation with a complete expansion and is therefore even above that of a quality-controlled load control.
In a further development according to the invention, the expansion machine can be coupled to an electric machine or a generator instead of to an internal-combustion engine, and the generated electric current can be fed to an electric storage device or directly to an electric consuming device.
In the case of a corresponding design, i.e. in order to operate the machine used for the load control in a variable manner as an expansion machine as well as a compressor or compression machine, the response behavior of the exhaust turbocharger can additionally be improved, and thereby an internal-combustion engine concept can be implemented that combines high power with a very favorable fuel consumption and, when an exhaust gas turbocharger is used, a very good response behavior (avoidance of a “turbo lag”).
Summarizing, the method according to the invention and the internal-combustion engine further developed according to the invention have the following advantages:
(a) very favorable fuel consumption with a high power potential and a very good response behavior when exhaust gas turbocharging;
(b) no high-expenditure internal internal-combustion engine techniques (such a variable valve timing) or burning methods (such as lean-burning methods with a correspondingly high-expenditure exhaust gas after treatment, HCCI, etc.) are required;
(c) the system (method and device) according to the invention can be represented without changing the internal-combustion engine concept (for example, on a TGDI internal-combustion engine (turbo gasoline direct injection)) by way of exclusively external measures (change-over flap, exhaust gas—combustion air—heat exchanger, expansion machine, charge air cooler);
(d) the burning method according to the invention is a conventional λ=1 burning method without any high-expenditure exhaust gas after treatment, and worldwide use of the invention will therefore be possible without any problems; and
(e) compared with the benefit, there are only minimal constructional expenditures and a very low technical risk.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of two preferred embodiments when considered in conjunction with the accompanying drawings.